1. Field of the Invention
The present invention relates to an addition curing type organopolysiloxane and its gel cured product excellent in adhesion to various substrates.
2. Description of the Prior Art
Because of their excellent electrical insulating properties, their excellent stability of the electrical properties, and their excellent flexibility, gel cured products of silicone rubbers are used for potting or sealing electrical and electronic parts, and particularly are used as a covering material for covering controlling circuit elements such as power transistors, IC, and condensers to protect them from being thermally or mechanically disordered.
As addition curing type organopolysiloxane compositions capable of forming silicone gels, various types are conventionally known.
For example, compositions that comprise an organopolysiloxane having vinyl groups bonded to silicon atoms and an organohydrogenpolysiloxane having hydrogen atoms bonded to silicon atoms and will be subjected to a crosslinking reaction in the presence of a platinum catalyst to provide a silicone gel are known (see Japanese Preexamination Patent Publication (Kokai) Nos. 143241/1981, 39659/1987, 35655/1988, and 33475/1988).
However, the above compositions that can be cured into gels and the gel cured products obtained therefrom are low in adhesion and therefore they have a defect that they are poor in adhesion to substrates. That is, where they are used in potting electrical and electronic parts, separation between the part and the gel cured product can occur, which causes a problem that moisture, water or the like penetrates therefrom and, for example, corrosion or defective insulation takes place.
On the other hand, Japanese Patent Publication (Kokoku) Nos. 13508/1978 and 21026/1978 teach that an adhesive elastomer is obtained by reacting an organopolysiloxane whose both ends are blocked with vinyl groups and an organohydrogenpolysiloxane having alkoxy groups and epoxy groups in the presence of a platinum compound. Further, Japanese Patent Publication (Kokoku) No. 43870/1985 teaches that an adhesive elastomer is obtained by using a vinyl group containing organopolysiloxane with trialkoxysilyl groups.
However, these are highly elastic elastomers and are completely different from gel cured products and if they are used as a protective material or an insulating material, for example, for semiconductor circuit elements, a thermal stress occurs in the elastomer itself due, for example, to the self-heat generation of the circuit element itself or the temperature environment where it is used, leading inevitably to a disadvantage that the semiconductor device or the like is broken.